Time domain reflectometer

ABSTRACT

A circuit is provided for sampling and accurately reproducing unknown signals, which could be electrical, optical, X-ray, gamma ray or particle signals, with picosecond resolution. The circuit comprises a superconductive sampling gate having at least two states which are distinguishable from one another and switching circuitry to switch the state of the sampling gate. The switching circuitry includes a sampling pulse source and a bias current source which are combined with the unknown signal to change the state of the monitor gate. A step generator utilizing Josephson junction technology is connected to the source of the unknown signal and sends a signal to the source of the unknown signal in order to initiate the outputting of the unknown signal and thus the sampling. Timing circuitry, also utilizing Josephson junction technology, provides an adjustable delay between the step signal generation and the sampling pulse generation.

TECHNICAL FIELD

The invention relates generally to apparatus and method for ultra-highresolution sampling of rapidly changing waveforms of output signalsgenerated by a signal source. In particular, the inventino relates to atime domain reflectometer system which utilizes Josephson junctiontechnology.

BACKGROUND OF THE INVENTION

The use of superconducting devices, and particularly Josephsontunnelling devices, in sampling or A/D circuits is already known in theart. Use of a Josephson device provide a very sensitive detectoroffering the possibility of very fast sampling speeds because such adevice is capable of extremely fast switching speed between two stablestates and because the device responds to extremely small magneticfields. U.S. Pat. No. 4,401,900 shows a Josephson sampling techniquewith a time resolution of 5 picoseconds and a sensitivity of 10microvolts. The time resolution of the described sampling system isextendable to the sub-picosecond domain, limited ultimately by theintrinsic switching speed of the Josephson device used as the samplinggate. In principle, the switching speed can be as fast as 0.09picoseconds. Josephson sampling techniques are not restricted to onlythose waveforms produced in a cryogenic environment. Rather, they can beused to measure waveforms from various sources, such as x-rays, opticalphotons or electrical waveforms produced by room-temperature sources, ifa suitable interface is available. Examples of such interfaces aredescribed in the co-pending patent applications Ser. No. 796,841,entitled "Room Temperature to Cryogenic Electrical Interface" filed onNov. 12, 1985 and Ser. No. 796,842, entitled "Open Cycle Cooling ofElectrical Circuits" filed on Nov. 12, 1985.

The Josephson sampling system described in U.S. Pat. No. 4,401,900comprises a superconductive monitor gate, such as a single Josephsondevice, which has at least two states distinguishable from one anotherand which is sensitive to the unknown waveform or signal to be sampled.Switching means, which includes the source of the unknown signal, asource of timing pulses, and a source of a bias signal, changes thestate of the monitor gate by a proper combination of the above signals.A timing means is provided to establish both a timing reference and anaccurate sampling delay time. The timing means includes a pulsegenerator for providing very short sampling pulses, delay lines, and asource of trigger pulses. The sampling system also has noise eliminationmeans to ensure the accuracy of the sample at any given instant of timeand a display to indicate the unknown waveform.

Sampling systems, however, are inadequate to accurately measurediscontinuities of network connections and to determine parameters ofcertain networks and devices. In such applications, time domainreflectometers, which comprise sampling circuitry with a step or pulsesource, are needed. Such a device usually supplies a pulse of a veryshort duration or a step with a very short rise time. The shorter therise time, the higher the time accuracy and the finer the details whichcan be measured by the sampling circuitry. The only time domainreflectometer system (TDR system) that is known to the applicants asbeing available commercially is manufactured by Tektronix, Inc. ofBeaverton, Oreg. as a plug-in module to its 7000 series oscilloscope.The TDR system consists of the sampling system plus a separate pulsegenerator and has a system rise time of more than 40 picoseconds.

One problem of existing TDR systems, such as the one described above, isthe relatively long system rise time which is inadequate for displayingrapidly changing waveforms. A second problem is that existing TDRsystems have the sampling circuitry separate from the pulse generator.Thus, if an existing superconducting sampling system is utilized toovercome the rise time problem, the pulse generator of the TDR systemwould be separate from, and only bonded to, the integrated circuit chipupon which the sampling circuitry is formed. Such a bond, however, hasbeen shown to have a reliability risk, as well as performancelimitations. Further, it has been shown by the aforementioned co-pendingapplications that the thermal, mechanical and electrical constraintsthat must be satisfied in order to perform superconducting sampling ofroom-temperature devices can be obviated by a monolithic chip having allthe particular circuitry and high performance transmission lines formedtheron.

SUMMARY OF THE INVENTION

The foregoing problems are obviated by the invention, comprising:

(a) means for generating and transmitting a trigger signal to the signalsource to initiate a transmission of the output signal to the samplingsystem;

(b) means for generating and introducing sampling pulses with thetransmission of the output signal to the sampling system;

(c) means for sampling the output signal comprising an adjustable biassignal source and a superconducting sampling gate having at least twodistinguishable states to which the output signal, said sampling pulsesand a bias signal provided by said adjustable bias signal source isapplied for switching the state of said gate in sampling the outputsignal; and

(d) means for providing an adjustable time delay in the application ofsaid sampling pulses with respect to the application of said triggersignal.

Advantageously, the use of superconducting sampling, employing, inparticular, Josephson junction technology, in a TDR system increases theswitching speed of such a system and obtains a system rise time of lessthan 10 picoseconds. In addition, the invention integrates on a singleintegrated circuit chip, a step generator, sampling circuitry, filterelements and ultrahigh performance transmission lines. Such a chip isoptimized with respect to satisfying electrical, thermal and mechanicalconstraints imposed by the extremely low operating temperatures at whichJosephson junction circuitry must function. Such a chip also achievesminimum jitter during the operation of the TDR system since all thecircuitry formed thereon, which already has reduced jitter as a resultof utilizing Josephson junction technology, is subject to the samerandom disturbances which may occur. Further, the invention provides fora novel step generator and novel delay mechanism which take advantage ofJosephson junction technology.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to thefollowing description of an exemplary embodiment thereof, and to theaccompanying drawings, wherein:

FIG. 1 is a schematic representation of the layout/architecture of anintegrated circuit chip having formed thereon a TDR system of thepresent invention;

FIG. 2 is an electrical schematic diagram of a TDR system of the presentinvention;

FIG. 2a is a graphical representation of the sampling operation of asampling gate of the TDR system of FIG. 2;

FIGS. 3a-3e are electrical schematic diagrams of several embodiments ofa step generator of the TDR system of FIG. 2;

FIG. 4a is an electrical schematic diagram of a buffer gate and a pulsegenerator gate of the TDR system of FIG. 2;

FIG. 4b is an electrical schematic diagram of a sampling gate and adelay gate of the TDR system of FIG. 2;

FIG. 4c is an electrical schematic diagram of an alternative embodimentof a delay generator of the TDR system of FIG. 2;

FIG. 5a is a schematic representation of the vertical profile of thestructure of the step generator of FIGS. 3a-3e;

FIG. 5b is a schematic representation of the vertical profile of thestructure of the pulse generator gate and the buffer gate of FIG. 4a;and

FIGS. 6a-6c are electrical schematic diagrams of several embodiments ofa TDR system of the present invention utilizing direct coupling.

DETAILED DESCRIPTION

FIG. 1 shows the layout/architecture of an integrated circuit chip 10that has formed thereon a TDR system of the present invention. The chip10 comprises an elongated substrate 11 whose material and physicaldimensions are dependent upon the particular application. Fabricated atone corner of the substrate 11 by a known method is a time domainreflectometer system (TDR system) 12 which utilizes Josephson junctioncircuitry. The area of the substrate 11 on which the TDR system 12 lies,as indicated by the dashed line in FIG. 1, is cooled to cryogenictemperatures, for example, according to the apparatus and method of theco-pending application Ser. Nos. 796,841 or 796,842; the remainingsubstrate 11 area is at room temperature. A number of non-criticalbiasing and monitoring lines 13, which may be of niobium or gold,connect to the TDR system 12 and extend most of the length of thesubstrate 11 to a group of connection or bonding pads 14 which act asthe low frequency interface for bonding to room temperature circuitryoff the chip 10. High performance transmission lines 15, 16, which alsomay be of niobium or gold, extend from the TDR system 12 to a highfrequency interface 17 at the other end of the substrate 11 whichconnects to a device under test (DUT) whose waveforms are to be sampledand measured. The physical constraints that the high performancetransmission lines 15, 16 must satisfy in order to maintain thenecessary performance for sampling and measuring are described in theco-pending application Ser. No. 796,841.

FIG. 2 is an electrical schematic diagram of a TDR system 20 of thepresent invention connected to a device under test (DUT) whose outputsignal waveform, I_(x) (t) is to be sampled and measured. The TDR system20 comprises a sampling gate 21 which has connected thereto a noisefilter circuit 21a and magnetically-coupled thereto an adjustable biascurrent circuit 21b, a portion of which may be off the chip 10. Thesampling gate 21 utilizes superconducting devices, such as a Josephsontunnelling device, to perform sampling of waveforms. Suchsuperconducting sampling gates are well known in the art, for example,as described in U.S. Pat. No. 4,401,900. A particular configuration ofthe sampling gate 21 is described in detail with respect to FIG. 4b.Note that the sampling gate 21 may also be connnected to other roomtemperature electronics including a display unit to view the DUTwaveform as well as other signal processing circuitry.

The TDR system 20 also comprises a pulse generator gate 22 which ismagnetically-coupled to the sampling gate 21 via a resistor22a-Josephson junction device J1 series and provides a samplng pulse,I_(p) to the sampling gate 21 via said coupling. The pulse generatorgate 22 is also tied to a noise filter circuit 22b and a first delaycircuit interface 24. A pulse generator gate which uses superconductingcircuitry is also well known in the art, for example, as described inU.S. Pat. No. 4,401,900. The first delay circuit interface 24 comprisesan inductor 24a which ties the pulse generator gate 22 to the remainderof the interface 24. The inductor 24a is connected to an external delaycircuit, Q_(pc) off the chip 10 via a low-pass resistor 24b-capacitor24c circuit. The inductor 24a is also connected, via a resistor 24d, toa Josephson junction device J2 which triggers the pulse generator gate22. The Josephson junction device J2 is tied to an external DC currentsource I_(pp) off the chip 10 via a low-pass resistor 24e-capacitor 24fcircuit in series with a noise filter 24g. The Josephson junction deviceJ2 is also tied directly to a delay generator 29 to be described later.

The TDR system 20 further comprises a step generator 25 which isconnected to a noise filter circuit 25a and, via a chip transmissionline 25b having a resistive termination 25c and the high performancetransmission lines 15, 16, is connected to the device under test (DUT).The chip transmission line 25b is magnetically-coupled to the samplinggate 21 and the pulse generator gate 22. The step generator 25 outputs avoltage step signal, I_(s) on the chip transmission line 25b with a fastrise time, e.g., less than 10 picoseconds, which is necessary in a highperformance electrical system such as a time domain reflectometer.Similar systems include logic circuit drivers and differentiating pulsegenerators. Several configurations for the step generator 25 utilizingJosephson junction technology are described with respect to FIGS. 3a-3e.

The step generator 25 is also magnetically-coupled to a step driver gateor buffer gate 26, via a resistor 26a-Josephson junction device J3series. The buffer gate 26 utilizes Josephson junction technology tosupply a trigger signal, I_(d) to the step generator 25 via saidmagnetic coupling. The buffer gate 26 is also connected to a noisefilter circuit 26b and a second delay circuit interface 28 which has thesame circuit configuration as the first delay circuit interface 24. Aninductor 28a ties the buffer gate 26 to the remainder of the interface28. The inductor 28a is connected, via a low-pass resistor 28b-capacitor28c circuit, to an external delay circuit, Q_(dc) off the chip 10. Notethat the connection to the external delay circuit Q_(dc) is preceded bya magnetic-coupling to the delay gate of delay generator 29. Theinductor 28a is also connected, via a resistor 28d, to a Josephsonjunction device J4 which triggers the buffer gate 26. The Josephsonjunction device J4 is tied to an external DC current source I_(dd) offthe chip 10 via a low-pass resistor 28e-capacitor 28f circuit in serieswith a noise filter 28g. The Josephson junction device J4 is alsodirectly tied to the delay generator 29.

Both interfaces 24, 28 are tied to the delay generator 29 via respectiveinput resistors 29a, 29b. The input resistors 29a, 29b are tied to acapacitor bank comprising a shunt resistor 29c-capacitor 29d series, afirst low-pass resistor 29e-capacitor 29f circuit and a second low-passresistor 29g-capacitor 29h circuit. The second low-pass circuit, inturn, is tied to a delay gate 29i. The delay gate 29i, which usessuperconducting circuitry, is magnetically-coupled to an externaltrigger source TRIG off the chip 10, via a noise filter 29k, and isconnected to the second delay circuit interface 28 as mentionedpreviously. The delay generator 29 is also connected to two noisefilters 29m, 29n. Note that all the noise filters of the TDR system 20,as well as the other described connections to external electronics, areconnected to electronics off the chip 10 via the biasing lines 13 shownin FIG. 1.

In operation, the buffer gate 26 and the associated Josephson junctiondevice J3 produce a pulse signal, I_(D) which triggers the stepgenerator 25 to output a step signal, I_(s) to the device under test(DUT). In response, the DUT then operates an output signal waveform,I_(x) (t) which is transmitted back along the chip transmission line25b. The pulse generator gate 22 and the associated Josephson junctiondevice J1 produce a sampling pulse, I_(p) which is applied to thesampling gate 21 via the magnetic-couple therebetween. The sampling gate21 is a threshhold device which will change its state when the summationof the inputs thereto exceeds a threshold value. As graphicallyillustrated by FIG. 2a, the sampling gate 21 thus uses the samplngpulse, I_(p) from the pulse generator gate 23, the output signalwaveform, I_(x) (t) and a bias current signal, I_(B) from the biascurrent circuit 21b in order to change its voltage state. Since thethreshold value is at a constant amplitude, the value of the biascurrent signal, I_(B) will track the amplitude of the output signalwaveform, I_(x) (t) if the amplitude of the sampling pulse, I_(p) isheld constant. In this manner, the output signal waveform, I_(x) (t) canbe reconstructed by the sampling gate 21 in both amplitude and shape toprovide an accurate reconstruction including both rise time and falltime increments of that signal.

The generation of the step signal, I_(s) and the introduction of thesampling pulse, I_(p), which sweeps across the step signal and theresulting output signal, I_(x) (t), and the timing or delay therebetweencan be implemented and adjusted in one of three ways by the TDR system20. An external delay can be produced by the trigger signal, delayedwith respect to one another, delivered from circuitry off the chip 10,i.e., the external delay circuits Q_(pc), Q_(dc), via the first andsecond delay circuit interfaces 24, 28. As can be seen from FIG. 2, theexternal delay circuits Q_(pc), Q_(dc) trigger the respective Josephsonjunction devices, J2, J4 which in turn trigger the respective gates 22,26. Such circuitry can change the power bias that affects the triggeringof the pulse generator gate 22 and the buffer gate 26, and thus, inturn, also the step generator 25. Note that the trigger signals areultimately derived from the TDR system 20 clock off the chip 10. On-chipdelay is provided by the switching of the delay gate 29i which causescharging of the capacitor bank of the delay generator 29. Theresistor-coupled capacitors are used to reduce internal resonances whichcould affect sweep linearity. As the capacitors charge, the currents ofthe trigger signals delivered from the external delay circuits Q_(pc),Q_(dc) and feeding to the Josephson junction devices J2, J4 of theinterfaces 24, 28 change. The switching of those devices are thendetermined by externally supplied currents from the external DC currentsources I_(pp), I_(dd) via the interfaces 24, 28 which compensate forthe change in current and thus control the triggering of the pulsegenerator gate 22 and the buffer gate 26. Note that initiation of atiming cycle, i.e., the switching of the delay gate 29i, is triggered bythe external trigger source TRIG whose signal is derived from the TDRsystem 20 clock off the chip 10. Another on-chip delay mechanism is toexternally supply the same trigger signal to the pulse generator gate 22and the buffer gate 26 but to produce the delay therebetween byadjusting the external DC current sources I_(pp), I_(dd) and, thus, thecurrents received by the first and second interfaces 24, 28. Thischanges the switching points of the associated Josephson junctiondevices J2, J4 and, thus, controls the triggering of the sampling pulseI_(p) and the step signal, I_(s).

Note that the use of Josephson junction devices by the TDR system 20provides the system with an inherent ability to reduce jitter duringwaveform sampling because a Josephson junction device's switchingthreshhold value is unambiguous. Furthermore, the present inventionimproves on existing systems by integrating the sampling gate 21, thepulse generator 22 and the step generator 25 on a single chip and, thus,minimizes the randomness of noise between the various inputs needed forsampling. The use of external delay circuits Q_(lpc), Q_(dc) achievessufficiently low jitter to provide a TDR system 20 resolution of below15 picoseconds; however,the described on-chip delay mechanism achieveeven lower jitter and provide better resolution if necessary. Suchsuperconducting delay mechanisms of the present invention thus provideminimum jitter without being cumbersome like mechanical delay lines orlimited to slowly changing waveforms like room temperature delaycircuitry.

FIGS. 3a through 3e show electrical schematic diagrams of severalembodiments of the step generator. FIG. 3a shows the basic configurationof a step generator 30 which comprises a configuration of triggerabledevices 31 which magnetically-couple to the buffer gate 26, such asinterferometers, and a network 33 which may be either purely resistiveor a connected series of Josephson junction devices. A resistor34-inductor 35 series connects the triggerable devices 31 to the network33. The network 33 is also directly connected to the chip transmissionline 36 having a resistive termination 37. FIG. 3b shows a simpleimplementation where the configuration of triggerable devices 31comprises one symmetric two-Josephson junction, magnetically-coupledinterferometer and the network 33 comprises a single Josephson junctiondevice.

FIG. 3c shows the configuration of triggerable devices 31 comprisingfour tightly coupled interferometers of FIG. 3b and the network 33comprising four Josephson junction devices connected in series. Such animplementation provides a step signal, I_(s) with greater voltageamplitude and provides better stability than a configuration having asmaller number of triggerable devices. This is accomplished because thetwo stage balanced pseudo-interferometer structures shown in FIG. 3ctend to lock the switching points of the four Josephson junction devicesand the fast rise time of the trigger pulse, I_(D) from the buffer gate26 ensures that the two balanced structures switch with very close timeproximity. The switching of the balanced structures causes the fourseries-connected junctions to switch simultaneously and rapidly, via theaction of the inductor 35, to produce the step signal, I_(s). Note thatwith the appropriate choice of component values, the step signal, I_(s)can have considerably lower rise time than that produced by the balancedstructures only. Rise times of the step signals achieved in the mannerdescribed are in the 6 picosecond range. FIG. 3d shows the configurationof triggerable devices 31 comprising a superconducting quantuminterference device (SQUID). FIG. 3e shows the configuration oftriggerable devices 31 comprising two tightly coupled interferometers ofFIG. 3b. Note that the number of triggerable devices in theconfiguration 31 does not need to be equal to the number of singleJosephson junction devices in the network 33.

In order to ensure that the triggerable devices 31 of the step generator30 switch simultaneously and in a very rapid time, e.g., shorter than 5picoseconds, the buffer gate 26 must supply enough current to switch thedevices 31 comfortably. FIG. 4a shows an electrical schematic diagram ofa buffer gate 40 which can provide such a fast control. The buffer gate40 comprises a symmetric two-Josephson junction, magnetically-coupledinterferometer as previously described with respect to FIG. 3b. Thepulse generator gate of the TDR system can utilize the same device andconfiguration since the circuit connections of both gates are similar.FIG. 4b shows the electrical schematic diagram of the sampling gate 45and the delay gate which can utilize the same circuity. Both gatescomprise s symmetric two-Josephson junction, magnetically-coupledinterferometer as described with respect to FIG. 3b but whoseorientation is reversed.

FIG. 4c shows a delay generator of the TDR system 20 which utilizesmulti-stage inductive coupling rather than capacitor charging to producea timing delay for the introduction of the sampling pulse, I_(p) by thepulse generator gate. The delay generator 47 comprises a plurality ofsymmetric two-Josephson junction, magnetically-coupled interferometers47a, as described with respect to FIG. 3b, which are magneticallycoupled to one another in a series. Each interferometer 47a has anassociated shunt resistor 47c inductor 47d series. The interferometers47a are also tied to a current source, which may be off the chip 10, vianoise filters (not shown). A delay control line 48a, shown runningadjacent to the interferometers, is connected to, for example, asawtooth generator off the chip 10. The trigger of the delay generator47 can be an inductively-coupled trigger or, as shown, can be theexternal delay circuit, Q_(pc) which is directly connected via alow-pass resistor 48b-capacitor 48c circuit. The output of the delaygenerator 47 can also be transmitted via magnetic-coupling, but, asshown, the output is directly tied to an inductor 48d which, in turn, istied to a pulse generator gate 49. With respect to FIG. 2, the delaygenerator 47 of FIG. 4c would be placed between the low-pass resistor24b-capacitor 24c circuit and the inductor 24a of the first delaycircuit interface 24. The remainder of the interface 24 would beeliminated as would the shown delay generator 29 and the second delaycircuit interface 28. In the case of the latter, the buffer gate 26would be tied to the external pulsed DC durrent source, I_(dd) via theinductor 28a. Thus, the delay generator 47 of FIG. 4c acts to onlyprovide a delay to the sampling pulse, I_(p) and not to the step signal,I_(s). In operation, the delay generator 47 provides a delay when thedelay control line 48a signals the interferometers 47a to change theirrespective switching points to thus control the triggering of the pulsegenerator gate 49. The total delay achieved is equal to the product ofthe number of interferometer stages and the delay of each stage. Notethat the interferometer stages may instead by directly connected toachieve the same operation.

FIG. 5a shows a schematic representation of a top view and two verticalprofiles of a step generator of the present invention as fabricated onthe substrate 11 of a chip 10. The top view of the step generator showsfour Josephson junction devices of the step generator formed on thesubstrate 11. A first vertical profile A shows the cross-section of theJosephson junction devices along line A--A. The profile A comprises athree layer base M1 having a thin layer of aluminum oxide (Al₂ O₃)sandwiched between two layers of niobium (Nb). The base M1 is patternedand anodized using niobium oxide (Nb₂ O₅) so as to leave exposed theareas upon which the Josephson junction devices are formed. A firstinterconnection lever M2 comprises niobium (Nb) is the next layer, suchthat the M1-M2 interfaces have the Josephson junction devicestherebetween. On the first interconnection level M2 is a resistor layer(not shown) and an insulating layer of silicon dioxide (SiO₂). A secondinterconnection level M3 is also comprised a niobium (Nb) which has agold (Au) contact layer formed thereon as shown. A second verticalprofile B shows the cross-section of the step generator along line B--B.FIG. 5b shows a schematic representation of a top view and a verticalprofile of a pulse generator gate and a buffer gate of the presentinvention which are both fabricated on the substrate 112 of a chip 10 inthe same manner. The top view of the gate shows two Josephson junctiondevices of the gate formed on the substrate 11. A vertical profile Cshows the cross-section of the Josephson junction devices along lineC--C and, although of a different configuration, is the same layeredstructure as described above for the step generator.

FIG. 6a shows an electrical schematic diagram of a TDR system 60 of thepresent invention which utilizes direct coupling between a sampling gate61 and the various input signal sources. The sampling gate 61 has acircuit configuration as shown in FIG. 4a and is tied to the deviceunder test (DUT) via a first chip transmission line 62 which has aresistive termination 63 therebetween. The sampling gate 61 is alsoconnected directly to an associated noise filter circuit 61b and a biascurrent circuit 61c. A pulse generator 64 is connected directly to thesampling gate 61 via a resistor 64a-Josephson junction device J1 series.A step generator 65 is connected directly to the DUT via a second chiptransmission line 66 having a resistive termination 67. The two chiptransmission lines 62, 66 are tied together to form one path to the DUT.Unlike the TDR system 20 of FIG. 2, the TDR system 60 of FIG. 6a splitsthe current of the step signal, I_(s) sent out by step generator 65 aswell as the current of the output signal, I.sub. x (t) of the DUT inorder to measure and sample the output signal waveform. A disadvantageof the "direct-coupled" TDR system of FIG. 6a is the super-imposingeffect on the transmission lines caused by the current splitting of thestep and output signals. However, the operation of the TDR system 60remains the same as previously described and sampling of an extremelyfast waveform is still possible. FIGS. 6b and 6c show otherconfigurations of direct-coupled TDR systems where the step generator 65is tied to the sampling gate 61 in different but operable manners. Inthese configurations, the step generator 65 comprises a configuration oftriggerable devices 65a with a network 65b shunted across. However,unlike the embodiments shown in FIGS. 3a-3c, there is no need forresistor and inductor components on the interconnection linetherebetween or on the chip transmission line. Further, the network 65bis optional. If used, the network 65b may be, for example, a resistivenetwork for matching the dynamics of the configuration of triggerabledevices 65a. The same limitations of FIG. 6a regarding performance alsohold true.

It is to be understood that the embodiments described herein are merelyillustrative of the principles of the invention. Various modificationsmay be made thereto by persons skilled in the art without departing fromthe scope or spirit of the invention.

What is claimed is:
 1. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for generating and transmitting a trigger signal to the signal source to initiate a transmission of the output signal to the sampling system; b. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; c. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; d. at least one superconducting switch, having at least two distinguishable states, that triggers the means for generating and transmitting a trigger signal to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and e. means for changing the switching point of the at least one superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 2. The device of claim 1, wherein the means for changing the switching point comprises:means for changing a power bias applied to the at least one superconducting switch so that the switching point of the at least one switch is adjustable and the triggering of the trigger signal and sampling pulse transmission can be adjustably delayed with respect to one another.
 3. The device of claim 1, wherein the means for changing the switching point comprises:means for changing a current feeding the at least one superconducting switch so that the switching point of the at least one switch is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 4. The device of claim 1, wherein the means for changing the switching point comprises:a delay generator comprising a switchable delay gate and a capacitor bank that charges in response to the switching of the delay gate, the charging of the capacitor bank changing the current feeding the at least one superconducting switch so that the switching point of the at least one switch is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 5. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for generating and transmitting a trigger signal to the signal source to initiate a transmission of the output signal to the sampling system; b. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; c. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; d. at least one superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, that triggers the means for generating and transmitting a trigger signal to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and e. means for changing the switching point of the at least one superconducting device displaying a Josephson tunnelling current so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 6. The device of claim 5, wherein the means for changing the switching point comprises:means for changing a power bias applied to the at least one superconducting device displaying a Josephson tunnelling current so that the switching point of the at least one device is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 7. The device of claim 5, wherein the means for changing the switching point comprises:means for changing a current feeding the at least one superconducting device displaying a Josephson tunnelling current so that the switching point of the at least one device is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 8. The device of claim 5, wherein the means of changing the switching point comprises:a delay generator comprising a switchable delay gate and a capacitor bank that charges in response to the switching of the delay gate, the charging of the capacitor bank changing the current feeding the at least one superconducting device displaying a Josephson tunnelling current so that the switching point of the at least one device is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 9. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for generating and transmitting a trigger signal to the signal source to initiate a transmission of the output signal to the sampling system; b. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; c. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied by switching the state of said gate in sampling the output signal; d. at least one superconducting device, comprising a Josephson junction and first and second electrodes on either side of the junction and having at least two distinguishable states, that triggers the means for generating and transmitting a trigger signal to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and e. means for changing the switching point of the at least one superconducting device so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 10. The device of claim 9, wherein the means for changing the switching point comprises:means for changing a power bias applied to the at least one superconducting device so that switching point of the at least one device is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 11. The device of claim 9, wherein the means for changing the switching point comprises:means for changing a current feeding the at least one superconducting device so that the switching point of the at least one device is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 12. The device of claim 9, wherein the means for changing the switching point comprises:a delay generator comprising a switchable delay gate and a capacitor bank that charges in response to the switching of the delay gate, the charging of the capacitor bank changing the current feeding the at least one superconducting device so that the switching point of the at least one device is adjustable and the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 13. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. a first superconducting switch, having at least two distinguishable states, that is capable of being triggered into switching action by a control signal; b. means for providing a control signal to the first superconducting switch to trigger the switch into switching action, said switching action generating a trigger signal that is transmitted to the signal source to initiate a transmission of the output waveform to the sampling system; c. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; d. means for sampling the output signal comprising an adjustable bias signal soruce and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; e. a second superconducting switch, having at least two distinguishable states, that triggers the means for providing a control signal to the first superconducting switch to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and f. means for changing the switching point of the second superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 14. The device of claim 13, wherein the means for providing a control signal comprises:a third superconducting switch, having at least two distinguishable states, that provides a control signal to the first superconducting switch to trigger the first switch into switching action, said switching action generating a trigger signal that is transmitted to the signal source to initiate a transmission of the output waveform to the sampling system.
 15. The device of claim 13, wherein the means for providing a control signal comprises:at least one superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, that provides a control signal to the first superconducting switch to trigger the switch into switching action, said switching action generating a trigger signal that is transmitted to the signal source to initiate a transmission of the output waveform to the sampling system.
 16. The device of claim 13, wherein the means for providing a control signal comprises:at least one superconducting device, comprising a Josephson junction and first and second electrodes on either side of the junction and having at least two distinguishable states, that provides a control signal to the first superconducting switch to trigger the switch into switching action, said switching action generating a trigger signal that is transmitted to the signal source to initiate a transmission of the output waveform to the sampling system.
 17. The device of claim 13, wherein the means for providing a control signal comprises:at least one symmetric, two-Josephson junction interferometer which is magnetically coupled to the first superconducting switch and which provides a control signal to the first superconducting switch to trigger the switch into switching action, said switching action generating a trigger signal that is transmitted to the signal source to initiate a transmission of the output waveform to the sampling system.
 18. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. at least one superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, that is capable of being triggered into switching action by a control signal; b. means for providing a control signal to the at least one superconducting device displaying a Josephson tunnelling current to trigger the device into switching action, said switching action generating a trigger signal that is transmitted to the signal source to initiate a transmission of the output waveform to the sampling system; c. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; d. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; e. at least one superconducting switch, having at least two distinguishable states, that triggers the means for providing a control signal to the at least one superconducting device to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and f. means for changing the switching point of the at least one superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 19. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. at least one superconducting device, comprising a Josephson junction and first and second electrodes on either side of the junction and having at least two distinguishable states, that is capable of being triggered into switching action by a control signal; b. means for providing a control signal to the at least one superconducting device to trigger the device into switching action, said switching action generating a trigger signal that is transmitted to the signal source to initiate a transmission of the output waveform to the sampling system. c. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; d. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; e. at least one superconducting switch, having at least two distinguishable states, that triggers the means for providing a control signal to the at least one superconducting device to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and f. means for changing the switching point of the at least one superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 20. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for transmitting signals between the sampling system and the signal source; b. a plurality of superconducting switches, each having at least two distinguishable states, connected in combination to the means for transmitting; c. a resistive network connected to the means for transmitting in parallel to the plurality of superconducting switches; d. means for providing a control signal to the plurality of superconducting switches to trigger the switches into switching action, said switching action generating a trigger signal that is transmitted to the signal source, via the means for transmitting, to initiate a transmission of the output waveform to the sampling system; e. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; f. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; g. at least one superconducting switch, having at least two distinguishable states, that triggers the means for providing a control signal to the plurality of superconducting switches to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and h. means for changing the switching point of the at least one superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 21. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for transmitting signals between the sampling system and the signal source; b. a plurality of superconducting switches, each having at least two distinguishable states, connected in combination to the means for transmitting; c. at least one superconducting switch, having at least two distinguishable states, connected to the means for transmitting in parallel to the plurality of superconducting switches; d. means for providing a control signal to the plurality of superconducting switches to trigger the switches into switching action, said switching action generating a trigger signal that is transmitted to the signal source, via the means for transmitting, to initiate a transmission of the output waveform to the sampling system; e. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; f. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; g. a second superconducting switch, having at least two distinguishable states, that triggers the means for providing a control signal to the plurality of superconducting switches to initiate a trigger signal transmission and the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and h. means for changing the switching point of the second superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 22. The device of claim 21, wherein the plurality of superconducting switches comprises:at least one symmetric, two-Josephson junction interferometer connected to the means for transmitting.
 23. The device of claim 21, wherein the plurality of superconducting switches comprises:a superconducting quantum interference device connected to the means for transmitting.
 24. The device of claim 21, wherein the plurality of superconducting switches comprises:a first symmetric, two-Josephson junction interferometer connected to the means for transmitting; and the means for providing a control signal comprises: a second symmetric, two-Josephson junction interferometer, which is magnetically-coupled to the first interferometer and which provides a control signal to the first interferometer to trigger the first interferometer into switching action, said switching action generating a trigger signal that is transmitted to the signal source, via the means for transmitting, to initiate a transmission of the output waveform to the sampling system.
 25. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for generating and transmitting a trigger signal to the signal source to initiate a transmission of the output signal to the sampling system; b. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; c. means for sampling the output signal comprising an adjustable bias signal source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; d. means for actuating the means for generating and transmitting a trigger signal to initiate a trigger signal transmission in a specified pulsed fashion; and e. at least one superconducting switch, having at least two distinguishable states, that actuates the means for generating and introducing sampling pulses to initiate a sampling pulse transmission a specified time after each trigger signal transmission.
 26. The device of claim 25, wherein the at least one superconducting switch comprises:at least one superconducting device displaying a Josephson tunnelling current.
 27. The device of claim 25, wherein the at least one superconducting switch comprises:at least one superconducting device, comprising a Josephson junction and first and second electrodes on either side of the junction.
 28. The device of claim 25, wherein the at least one superconducting switch comprises:a delay generator comprising a plurality of symmetric, two-Josephson junction interferometers, which are magnetically-coupled to one another in a series, and means for controlling the respective switching points of the plurality of interferometers, the output of said delay generator actuating the means for generating and introducing sampling pulses to initiate a sampling pulse transmission a specified time period after each trigger signal transmission.
 29. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. a first superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which generates and transmits a trigger signal upon switching states to the signal source to initiate a transmission of the output signal to the sampling system; b. a second superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which provides a control signal to the first superconducting device to cause the first superconducting device to switch states and thereby generate and transmit a trigger signal; c. means for generating and introducing sampling pulses with the transmission of the output signal to the sampling system; d. means for sampling the output signal comprising an adjustable bias source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal; e. a third superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which triggers the second superconducting device to provide a control signal to the first superconducting device to initiate a trigger signal transmission and which triggers the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and f. means for changing the switching point of the third superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 30. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for transmitting signals between the sampling system and the signal source; b. a first superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which generates and transmits a trigger signal upon switching states to the signal source via the means for transmitting to initiate a transmission of the output signal to the sampling system; c. a second superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which provides a control signal to the first superconducting device, via a magnetic-coupling therebetween, to cause the first superconducting device to switch states and thereby generate and transmit a trigger signal; d. a pulse generator which introduces sampling pulses, via a magnetic-coupling to the means for transmitting, with the transmission of the output signal to the sampling system; e. means for sampling the output signal comprising an adjustable bias source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses, and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal, said gate receiving the output signal from the means for transmitting and the sampling pulses from the pulse generator from respective magnetic-couples therebetween; f. a third superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which triggers the second superconducting device to provide a control signal to the first superconducting device to initiate a trigger signal transmission and which triggers the pulse generator to initiate a sampling pulse transmission; and g. means for changing the switching point of the third superconducting device so that the triggering of the trigger signal and the sampling pulse transmissions can be adjustably delayed with respect to one another.
 31. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for transmitting signals between the sampling system and the signal source; b. a first superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which is directly connected to a first point of the means for transmitting and which generates and transmits a trigger signal upon switching states to the signal source to initiate a transmission of the output signal to the sampling system; c. a second superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which provides a control signal to the first superconducting device, via a magnetic-coupling therebetween, to cause the first superconducting device to switch states and thereby generate and transmit a trigger signal; d. a pulse generator which introduces sampling pulses, via a direct connection to the first point of the means for transmitting, with the transmission of the output signal to the sampling system; e. means for sampling the output signal comprising an adjustable bias source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses, and a bias signal provided by said adjustable bias signal source is applied for switching the state of said gate in sampling the output signal, said gate receiving the output signal and the sampling pulses from the pulse generator from a direct connection to the first point of the means for transmitting; f. a third superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which triggers the second superconducting device to provide a control signal to the first superconducting device to initiate a trigger signal transmission and which triggers the pulse generator to initiate a sampling pulse transmission; and g. means for changing the switching point of the third superconducting device so that the triggering of the trigger signal and the sampling pulse transmissions can be adjustably delayed with respect to one another.
 32. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for transmitting signals between the sampling system and the signal source; b. a first superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, comprising a plurality of superconducting switches directly connected in combination to a first point of the means for transmitting and a resistive network connected in parallel to the combination, said device generating and transmitting a trigger signal upon switching states to the signal source to initiate a transmission of the output signal to the sampling system; c. a second superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which provides a control signal to the first superconducting device, via a magnetic-coupling therebetween, to cause the first superconducting device to switch states and thereby generate and transmit a trigger signal; d. a pulse generator which introduces sampling pulses, via a direct connection to the first point of the means for transmitting, with the transmission of the output signal to the sampling system; e. means for sampling the output signal comprising an adjustable bias source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses, and a bias signal provided by the adjustable bias signal source is applied for switching the state of said gate in sampling the output signal, said gate receiving the output signal and the sampling pulses from the pulse generator from a direct series connection with the resistive network of the first superconducting device; f. a third superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which triggers the second superconducting device to provide a control signal to the first superconducting device to initiate a trigger signal transmission and which triggers the pulse generator to initiate a sampling pulse transmission; and g. means for changing the switching point of the third superconducting device so that the triggering of the trigger signal and the sampling pulse transmissions can be adjustably delayed with respect to one another.
 33. A system for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. means for transmitting signals between the sampling system and the signal source; b. a first superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, comprising a plurality of superconducting switches directly connected in combination to a first point of the means for transmitting and a resistive network connected in parallel to the combination, said device generating and transmitting a trigger signal upon switching states to the signal source to initiate a transmission of the output signal to the sampling system; c. a second superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which provides a control signal to the first superconducting device, via a magnetic-coupling therebetween, to cause the first superconducting device to switch states and thereby generate and transmit a trigger signal; d. a pulse generator which introduces sampling pulses, via a direct connection to the first point of the means for transmitting, with the transmission of the output signal to the sampling system; e. means for sampling the output signal comprising an adjustable bias source and a superconducting sampling gate having at least two distinguishable states to which the output signal, said sampling pulses, and a bias signal provided by the adjustable bias signal source is applied for switching the state of said gate in sampling the output signal, said gate receiving the output signal and the sampling pulses from the pulse generator from a direct series connection with the combination of plurality of superconducting switches of the first superconducting device; f. a third supeconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, which triggers the second superconducting device to provide a control signal to the first superconducting device to initiate a trigger signal transmission and which triggers the pulse generator to initiate a sampling pulse transmission; and g. means for changing the switching point of the thrid superconducting device so that the triggering of the trigger signal and the sampling pulse transmissions can be adjustably delayed with respect to one another.
 34. A method for high resolution sampling of the waveform of an output signal generated by a signal source, comprising:a. generating and transmitting a trigger signal from a first superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, to the signal source to initiate a transmission of the output signal to the sampling system; b. providing a control signal from a second superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, to the first superconducting device to cause the first superconducting device to switch states and thereby generate and transmit a trigger signal; c. generating and introducing sampling pulses with the transmission of the output signal to the sampling system; d. sampling the output signal by applying the output signal, said sampling pulses and a bias signal provided by an adjustable bias signal source to a superconducting sampling gate having at least two distinguishable states for switching the state of said gate in sampling the output signal; e. triggering the second superconducting device, via a third superconducting device displaying a Josephson tunnelling current, having at least two distinguishable states, to provide a control signal to the first superconducting device to initiate a trigger signal transmission and triggering the means for generating and introducing sampling pulses to initiate a sampling pulse transmission; and f. changing the switching point of the third superconducting switch so that the triggering of the trigger signal and sampling pulse transmissions can be adjustably delayed with respect to one another.
 35. A system for high resolution sampling of the electrical waveform of a signal transmitted from a signal source, comprising:a. a substrate having a first portion capable of being cooled to a cryogenic temperature while simultaneously having a second portion at a second temperature; b. means for measuring and storing the instantaneous value of the waveform of a signal transmitted from a signal source, said means for measuring and storing being formed on the first portion of the substrate; c. means for transmitting signals between the means for measuring and storing and the signal source; d. means for applying an incident signal to the signal source to initiate a transmission of a signal to the means for measuring and storing, said means for applying being formed on the first portion of the substrate; e. means for adjustably delaying the application of an incident signal by the means for applying with respect to the measuring and storing the instantaneous value of the signal waveform by the means for measuring and storing. 